Physical and Chemical Characterization of Dust Deposited in the Turan Lowland
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e3sconf caduc2019 03005
1 Introduction and Study Design
Water is a valuable resource and has to be managed efficiently, especially in Central Asia, a land-locked arid region with a population of 65.3 million. The water required for sustaining this fragile system comes from the Central Asian “water towers” [1] – the highly glaciated mountain areas of the Pamir and Tien Shan mountains. From there it feeds the two large Central Asian streams, the Amu-Darya and Syr-Darya. Together with the Aral Sea as their terminal lake they form the largest inland watershed worldwide [2, 3]. Steep mountain slopes, thin soils and low evaporation rates in the upper catchments lead to a rapid surface runoff, especially during the snow and glacier melt period in spring and summer, creating a good water supply in a region with overall little precipitation [4]. This combination of abundant water supply during the vegetative period and a hot and dry climate in the lowlands is well suited for agriculture. This was the basis for the elaboration of traditional irrigation schemes and the development of rich oasis cities in the land between those two streams (Transoxania = “Beyond the Oxus River”, the Oxus being an old name for the Amu-Darya) dating back for more than two millennia [5]. During the 20th century the land and water use intensified beyond sustainable measures and grand irrigation farming and hydropower plans were implemented. This overexploitation of the water resources led to a sizeable annual water deficit and to the largest man-made ecological disaster, known as the Aral Sea syndrome [6- 9]. As less and less water reached the Aral Sea and the evaporation surpassed the freshwater inflow, the water volume and lake surface decreased, increasing the salinity of the lake’s water to toxic levels (from 10.2 g/l in 1947 to 80.0 g/l in 2005 [10]). The extensive use of agrochemicals (fertilizers based on Ammonium, Nitrogen, Phosphor and Potassium, pesticides like DDT, Phosalone, Lindane or Toxaphene [11]) and salts leached from salinized fields in the Aral Sea basin further contributed to the accumulation of hazardous substances in the lake for many decades [6, 12-18]. The desiccation of the Aral Sea exposed the polluted lake bed sediments to the forces of the wind. The lake turned into a desert – the Aralkum, covering more than 60,000 km² (Fig. 1) [6, 7, 19] – and wind erosion now remobilizes the salts and agrochemicals deposited in the lake over decades. These airborne pollutants are a potential health risk for the region surrounding this man-made desert [6, 7, 15, 20] and require a thorough monitoring. Due to the remoteness and size of the affected area of more than 1.5 million km² spread out predominately over three E3S Web of Conferences 99, 03005 (2019) https://doi.org/10.1051/e3sconf/20199903005 CADUC 2019 © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). countries (Kazakhstan, Turkmenistan, Uzbekistan) most studies focus on remote sensing as their primary data for the monitoring of the aeolian sediment transport [21-24]. But while satellite data can provide an area-wide quantification of the transported material and can also provide insights into the qualitative nature of the airborne dust due to its spectral characteristics, on-site measurements of the dust deposition and laboratory analyses of its mineralogical and chemical properties are needed to complement such a monitoring. Fig. 1. Dust sampling sites and the three major dust sources Karakum, Kyzylkum and Aralkum The study presented here collected monthly dust deposition samples from 23 meteorological stations in four regions (Aralkum, Khorezm, Karakum and Kyzylkum; Fig. 1) between 2006 and 2012. All collected dust samples (inverted Frisbee design passive deposition samplers in 3 m height; [6]) were weighted and selected samples (based on the available sample material) were used for the analyses of the grain size composition the mineral composition (using wavelength dispersive X-ray diffraction), and the chemical composition (using atomic absorption spectroscopy and X-ray fluorescence). Download 393.45 Kb. Do'stlaringiz bilan baham: |
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